The present invention relates to an alloy strengthened by dispersion of particles of a metal and an intermetallic compound. The present invention also relates to a process for producing such a dispersion-strengthened alloy.
Aluminum alloys are lightweight and have superior mechanical characteristics but they are not highly wear-resistant. There are two approaches to improve the wear resistance of aluminum alloys; one approach depends on working their surface and the other is directed to modifying the bulk material itself. One of the methods known in the art that belongs to the second approach comprises dispersing highly wear-resistant particles in the aluminum alloy.
Ni powder is an oxidation-resistant powder, and an Al-Ni base intermetallic compound powder is also resistant to oxidation and has a high degree of hardness. These powders have good affinity and hence good wettability with matrix materials of Al-Ni base alloy and exhibit high stability therein. Si powder is also resistant to oxidation and has a high degree of hardness. This powder has good wettability with matrix materials of Al-Si-Cu base alloy.
The Ni powder, Si powder and the intermetallic compound powder described above will dissolve very quickly when they are directly added to the melt of a prior art aluminum alloy such as an Al-Si base alloy or an Al-Si-Cu base alloy. Therefore, alloys strengthened by dispersion of particles of a metal and an intermetallic compound are conventionally produced by sintering techniques. In the sintering method conventionally employed, a metal powder or an intermetallic compound powder is added to the fine particles of a matrix forming metal, and the mix attained by mechanical agitation is pressed into a compact which then is sintered at elevated temperatures to produce a dispersion-hardened alloy strengthened by particles of the added metal or intermetallic compound. This alloy is subsequently fabricated into the final product either with an extruder or a rolling mill.
However, the conventional sintering technique has two serious problems. First, it is difficult to uniformly disperse the particles of a metal powder or an intermetallic compound powder in the powder of a matrix-forming mother alloy by mechanical agitation because the added particles will agglomerate and because they have a different specific gravity from the matrix particles. Secondly, in order to prevent the occurrence of oxidation which is accompanied with the pressing of the powder mix into a compact and subsequent sintering at elevated temperatures, an oxidation-preventing method and apparatus must be employed at the stage of sintering. This offers a certain constraint on the efforts to attain products having high dimensional accuracy and strength. Furthermore, the use of the oxidation-preventing apparatus considerably increases the overall cost of the process. Therefore, it has been difficult to produce large quantities of dispersion-hardened alloys at low cost by sintering techniques.
Under these circumstances, it has been desired to develop a dispersion-hardened alloy having superior mechanical properties that can be produced by a simple method and which has particles of a metal or an intermetallic compound dispersed quite uniformly in a mother alloy.